Measurements of Higgs boson properties in thediphoton decay channel with 36 fb −1 of p p collision data at √ s = 13 TeV with the ATLAS detectorThe ATLAS CollaborationProperties of the Higgs boson are measured in the two-photon final state using 36.1 fb −1 of proton-proton collision data recorded at √ s = 13 TeV by the ATLAS experiment at the Large Hadron Collider. Cross-section measurements for the production of a Higgs boson through gluon-gluon fusion, vector-boson fusion, and in association with a vector boson or a top-quark pair are reported. The signal strength, defined as the ratio of the observed to the expected signal yield, is measured for each of these production processes as well as inclusively. The global signal strength measurement of 0.99 ± 0.14 improves on the precision of the ATLAS measurement at √ s = 7 and 8 TeV by a factor of two. Measurements of gluon-gluon fusion and vector-boson fusion productions yield signal strengths compatible with the Standard Model prediction. Measurements of simplified template cross sections, designed to quantify the different Higgs boson production processes in specific regions of phase space, are reported. The cross section for the production of the Higgs boson decaying to two isolated photons in a fiducial region closely matching the experimental selection of the photons is measured to be 55±10 fb, which is in good agreement with the Standard Model prediction of 64 ± 2 fb. Furthermore, cross sections in fiducial regions enriched in Higgs boson production in vector-boson fusion or in association with large missing transverse momentum, leptons or top-quark pairs are reported. Differential and double-differential measurements are performed for several variables related to the diphoton kinematics as well as the kinematics and multiplicity of the jets produced in association with a Higgs boson. These differential cross sections are sensitive to higher order QCD corrections and properties of the Higgs boson, such as its spin and CP quantum numbers. No significant deviations from a wide array of Standard Model predictions are observed. Finally, the strength and tensor structure of the Higgs boson interactions are investigated using an effective Lagrangian, which introduces additional CP-even and CP-odd interactions. No significant new physics contributions are observed. 9 Measurement of fiducial integrated and differential cross sections 53 9.1 Particle-level fiducial definition of the Higgs boson diphoton cross sections 53 9.2 Fiducial integrated and differential cross sections 54 9.3 Measurements of cross sections of fiducial integrated regions 56 9.4 Measurements of cross sections of inclusive and exclusive jet multiplicities 62 9.5 Measurements of differential and double-differential cross sections 63 9.5.1 Measurements of cross sections probing the Higgs boson production kinematics 63 9.5.2 Measurements of cross sections probing the jet kinematics 65 9.5.3 Measurements of cross sections probing spin and CP 66 9.5.4 Cross sections probing the VBF production mode 68 9....

ggF H→ττ = 3.1 ± 1.0 (stat.) +1.6 −1.3 (syst.) pb, respectively. Similarly, results of a fit are reported in the framework of simplified template cross sections. All measurements are in agreement with Standard Model expectations.The ATLAS and CMS collaborations discovered [1, 2] a particle consistent with the Standard Model (SM) [3][4][5] Higgs boson [6][7][8][9][10] in 2012. Several properties of this particle, such as its coupling strengths, spin and charge-parity (CP) quantum numbers, were studied with 7 and 8 TeV center-of-mass energy ( √ s) proton-proton collision data delivered by the Large Hadron Collider (LHC) in 2011 and 2012, respectively, referred to as 'Run 1'. These results rely predominantly on studies of the bosonic decay modes [11][12][13][14] and have not shown any significant deviations from the SM expectations.The coupling of the Higgs boson to the fermionic sector has been established with the observation of the H → ττ decay mode with a signal significance of 5.5σ from a combination of ATLAS and CMS results [15][16][17] using LHC Run-1 data. A measurement performed by the CMS Collaboration with Run-2 data at √ s = 13 TeV reached a significance of 4.9σ using 35.9 fb −1 of integrated luminosity and 5.9σ combined with data from Run 1 [18]. While the Higgs-boson coupling to other fermions such as top quarks [19, 20] and bottom quarks [21, 22] have been observed, only upper limits exist on its coupling to muons [23, 24] and the H → ττ decay mode has been the only accessible leptonic decay mode. It was also used to constrain CP violation in the production via vector-boson fusion (VBF) [25] and is unique in that it provides sensitivity to CP violation in the Higgs-boson coupling to leptons [26]. This paper presents cross-section times branching-fraction measurements of Higgs bosons that decay into a pair of τ-leptons in proton-proton (pp) collisions at √ s = 13 TeV using data collected by the ATLAS experiment in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb −1 . All combinations of leptonic (τ → νν with = e, µ) and hadronic (τ → hadrons ν) τ decays are considered.1 The corresponding three analysis channels are denoted by τ lep τ lep , τ lep τ had and τ had τ had and are composed of different dominant backgrounds. While Z → ττ is a dominant background in all channels, the relative contributions from other backgrounds from top-quark and other vector-boson decays, as well as from misidentified leptonic or hadronic τ decays, vary considerably between the channels. Two analysis categories are defined that are predominantly sensitive to Higgs bosons produced via VBF and gluon-gluon fusion (ggF). A maximum-likelihood fit is performed on data using distributions of the reconstructed di-τ mass in signal regions (SRs), simultaneously with event yields from control regions (CRs) that are included to constrain normalizations of major backgrounds estimated from simulation. The dominant and irreducible Z → ττ background is estimated from simulation. This is different from the search for H...

This Letter presents a measurement of γγ → μ þ μ − production in Pb þ Pb collisions recorded by the ATLAS detector at the Large Hadron Collider at ffiffiffiffiffiffiffi ffi s NN p ¼ 5.02 TeV with an integrated luminosity of 0.49 nb −1. The azimuthal angle and transverse momentum correlations between the muons are measured as a function of collision centrality. The muon pairs are produced from γγ through the interaction of the large electromagnetic fields of the nuclei. The contribution from background sources of muon pairs is removed using a template fit method. In peripheral collisions, the muons exhibit a strong back-to-back correlation consistent with previous measurements of muon pair production in ultraperipheral collisions. The angular correlations are observed to broaden significantly in central collisions. The modifications are qualitatively consistent with rescattering of the muons while passing through the hot matter produced in the collision.

A search for new heavy particles that decay into top-quark pairs is performed using data collected from proton–proton collisions at a centre-of-mass energy of 13  by the ATLAS detector at the Large Hadron Collider. The integrated luminosity of the data sample is 36.1 fb. Events consistent with top-quark pair production are selected by requiring a single isolated charged lepton, missing transverse momentum and jet activity compatible with a hadronic top-quark decay. Jets identified as likely to contain b-hadrons are required to reduce the background from other Standard Model processes. The invariant mass spectrum of the candidate top-quark pairs is examined for local excesses above the background expectation. No significant deviations from the Standard Model predictions are found. Exclusion limits are set on the production cross-section times branching ratio for hypothetical bosons, Kaluza–Kein gluons and Kaluza–Klein gravitons that decay into top-quark pairs.

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